Concrete bridge deckings are commonly coated with a protective layer of asphalt (up to 15 cm thick), uniformly spread under heavy rolling equipment, which may weigh 10 metric tons or more. This asphalt layer is exposed to extremes of weather throughout the year, and will eventually develop cracks, some so small as to be practically invisible, others much larger. All are harmful, in that they permit liquid water to penetrate down to the concrete surface, where it freezes in winter and causes sizable portions of the asphalt layer to spall away. These adverse factors (freeze-shattering, traffic impact, chloride disintegration from de-icing salt, etc.) result in serious damage to the concrete traffic surface and eventually require major repairs.
Aside from asphalt-coated concrete surfaces, bridge concrete in the form of superstructure, parapets, crash barriers, etc., is also subject to attack, viz., from air- or moisture-borne industrial chemicals; spattered de-icing salt; and carbonation, i.e., gradual penetration of atmospheric carbon dioxide which then reacts with the alkaline materials in the concrete and attacks reinforcement in the concrete.
To inhibit the aforesaid destruction, it is conventional in concrete bridge construction and maintenance to apply a bridge deck membrane (BDM) to the concrete surface before laying down asphalt. Several BDM's are available. Polyurethane has been tried.
A BDM should meet a number of technical and economic criteria. It should:
(1) be impermeable to liquid water from above, yet be sufficiently permeable to permit small amounts of water vapor to escape from the concrete substrate; PA1 (2) be solventless; PA1 (3) be easily applied, preferably sprayable; PA1 (4) have good adhesion to concrete; PA1 (5) have low chloride penetration; PA1 (6) be stable to concrete alkali; PA1 (7) be stable under conditions of asphalt application - hard, but not brittle, yet be sufficiently flexible to cope with dimensional changes generated by temperature differentials and bridge movements; be able to tolerate application of asphalt at 170.degree. under a 10-ton roll; PA1 (8) provide superior adhesion of asphalt as applied to the BDM; PA1 (9) be resistant to asphalt migration (i.e., tendency of low molecular weight hydrocarbons in asphalt to migrate into the BDM, weakening and/or destroying it). PA1 (10) have competitive raw material costs; PA1 (11) not discolor concrete; PA1 (12) have prolonged life on exposed surfaces (e.g., vertical surfaces and other surfaces not asphalt-coated); PA1 (13) be tough enough within a reasonable time for construction crews to walk on it. PA1 Glycerol (92) preferred PA1 Butanetriol-1,2,3 (106) PA1 Trimethylolethane (120) PA1 Pentaglycerol (120) PA1 Erythritol (122) PA1 Trimethylolpropane (134) PA1 Pentaerythritol (136) PA1 Triethanolamine (149) PA1 Triethanolpropane (176) PA1 Triethylene diamine PA1 N-methyl morpholine PA1 N-ethyl morpholine PA1 Diethyl ethanolamine PA1 1-methyl-4-dimethylamino ethyl piperazine PA1 3-methoxy-N-dimethyl propyl amine PA1 N-dimethyl-N'-methyl isopropyl propylene diamine PA1 N,N-diethyl-3-diethyl amino propylamine PA1 N,N-dimethyl benzyl amine PA1 Dicyclohexylmethylamine PA1 2,4,6-tris dimethylaminomethylphenol PA1 N,N-dimethyl cyclohexylamine PA1 Triethylamine PA1 Tri-n-butylamine PA1 1,8-diaza-bichloro[5,4,0]-undecene-7 PA1 N-methyl diethanolamine PA1 N,N-dimethyl ethanolamine PA1 N,N-dimethyl cyclohexylamine PA1 N,N,N'N'-tetramethyl-ethylene diamine PA1 1,4-diaza-bicyclo-[2,2,2]-octane PA1 N-methyl-N'-dimethylaminoethyl-piperazine PA1 Bis-(N,N-diethylaminoethyl)-adipate PA1 N,N-diethylbenzylamine PA1 Pentamethyldiethylene triamine PA1 N,N,N'-tetramethyl-1,3-butanediamine PA1 1,2-dimethylimidazole PA1 2-methylimidazole PA1 Stannous chloride PA1 Dibutyl tin di-2-ethyl hexoate PA1 Stannous octoate PA1 Dibutyl tin dilaurate PA1 Trimethyl tin hydroxide PA1 Dimethyl tin dichloride PA1 Dibutyl tin diacetate PA1 Dibutyl tin oxide PA1 Tributyl tin acetate PA1 Tetramethyl tin PA1 Dimethyl dioctyl tin PA1 Tin ethyl hexoate PA1 Tin laurate PA1 Dibutyl tin maleate PA1 Dioctyl tin diacetate PA1 Zinc octoate PA1 Phenyl mercuric propionate PA1 Lead octoate PA1 Lead naphthenate PA1 Copper naphthenate PA1 (1) the novel combination of Components A and B as set forth in generic and specific formulations herein; PA1 (2) the processes (generic and specific) of mixing together Components A and B aforesaid; PA1 (3) the resins (generic and specific) resulting from (2) above; PA1 (4) process of coating a substrate with the resins of (3) above. Substrates of particular interest are metals and concrete, e.g., bridge decking. PA1 (5) coated metal or concrete articles resulting from (4) above; PA1 (6) overall process of protecting metals or concrete bridge decking by applying the resins of (3) above to metals or concrete, as the case may be; PA1 (7) as an article, bridge decking comprising concrete-polyurethane-asphalt laminate, the polyurethane being the resin of (3) above.
An undated technical brochure entitled .music-flat.Desmophen", available from Mobay Chemical Co., describes "Desmophen".RTM. as a "branched polyalcohol with ether and ester groups". The brochure discloses that Desmophen.RTM. can be reacted with isocyanates (not defined) to make polyurethane coatings for concrete. The coating formulation must include molecular sieve zeolites "for thorough drying" (p. 12), and may include fillers. The coating is said to be hard and moisture resistant. There is no teaching of added elastomers. Prior to use on concrete, a primer is applied to the concrete (p. 13). The polyurethane coating may be applied to cast asphalt floorings and to steel and "bridge structures" (p. 14). Our analyses indicate that "Desmophen" contains castor oil.
Castor oil is known as a polyol reactant with diisocyanates to form urethanes. Ency. Pol. Sci. and Techn. 3, 25 (1965). Glycerol is reported to react with castor oil to transesterify the ricinoleic triglyceride molecules, providing a polyol glyceride mixture for reaction with hexamethylene diisocyanate. Op. cit. 11, 514 (1969); Chem. Abs. 36:6270.sup.2.
In a brochure entitled "Bayer Engineering Polymers: (apparently dated November, 1985), Bayer UK Limited offers commercially a polyurethane made from a polyether polyol (Component A) and a modified MDI (Component B). The composition is not further given. The two components are mixed at the site, e.g., by spraying, on bridge decking or other concrete surface. The applied resin is said to cure tack-free in a few minutes and can be walked on in 20-30 minutes.
In a technical brochure on "352-Oldopren-S" (apparently dated March, 1983), Buesing & Fasch GmbH & Co. of Oldenburg, Germany, describe an MDI-based 2-component, polyurethane that provides an elastic film, useful (under asphalt) on road- and bridge-concrete surfaces.
R. I. Frascoia describes the use of four polyurethane membranes in bridge deck systems in an article, "Field Performance of Experimental Bridge Deck Membrane Systems in Vermont", Transportation Research Record, pp. 57-65 (1984). Three of the polyurethanes were asphalt-modified. Formulations are not otherwise given. Bond between bituminous pavement and membrane was rated "Poor", but overall performance was rated "Fair to Good".
Use of an "asphalt-extended urethane membrane" is described in an article b A. L. Meader, Jr. et al, "Development of a Cold-Poured Bridge Deck Membrane System", ASTM Special Technical Publications N 629, pp. 164-177 (1976).
For a good review article, especially for UK practice, see M. D. McDonald, "Concrete Bridge Deck Waterproofing Systems: in Highways and Road Construction", pp. 26-30 (August 1973). According to the article, polyurethane is blended with pitch to improve low-temperature flexibility and to reduce raw material costs; the membrane may need an epoxy primer (on concrete) and may need a surface protective layer before rolling on the final asphalt coating. "Cracking" and "chisel" tests are described.
An undated brochure, "Poly bd.RTM. Resins in Urethane Elastomers", released by Arco Chemical Co., discloses dihydroxyl-terminated polybutadiene and its reaction with aromatic diisocyanates. Page 3 of the brochure discloses a polybutadiene, "R-45HT", with structural formula, indicating the molecular weight to be about 2,800. (This polybutadiene was used in Examples 1 and 2 below.)
In a technical bulletin, "Hycar Reactive Liquid Polymers" released by BFGoodrich Co. (apparently dated March, 1981), Hycar polymer is described as an acrylonitrile-based diol that can be reacted with MDI to provide low temperature flexibility and chemical resistance.
U. S. Pat. No. 4,680,203 (1987) discloses a polyurethane coating for bridge concrete, prepared from polyols and MDI. The polyols can be a mixture of poly(propylene oxide) (col. 1, line 65), glycerine (col. 2, line 3), and acrylonitrile-butadiene copolymer (col. 2, line 35).
U. S. Pat. No. 4,689,268 (1987) discloses a 3-layer laminate on concrete, viz., epoxy resin plus filler, a bonding agent, and a polyurethane.
U. S. Pat. No. 4,559,239 (1985) describes a 2-component (polyol-MDI) polyurethane applicable to concrete.
U. S. Pat. No. 3,725,355 discloses glycerine, polyether polyol, and an isocyanate prepolymer. The polyol can be a triol and must have a molecular weight of at least 2,000.
U. S. Pat. No. 4,507,336 (1985) describes a 2-component ("A" and "B") polyurethane, sprayable as a roof coating. "A" is (e.g.) a liquid modified MDI plus a chlorinated paraffin; "B" comprises (e.g.) a polypropylene glycol, 1,4-butanediol, and dibutyltin dilaurate catalyst.
Canadian Patent No. 927,642 (1973) describes applying a polyurethane foam directly to a roadbed (not to concrete), followed by a bitumen layer on the polyurethane foam.
The combination of MDI and poly(propylene oxide) triol is disclosed, e.g., in U. S. Pat. Nos. 3,515,699, 4,532,316, and 4,604,445. The combination of glycerol and poly(propylene oxide) triol is disclosed in U. S. Pat. Nos. 3,993,576 and 4,410,597, and the combination of MDI and glycerol in U.S. Pat. No. 4,145,515. Glycerol, poly(propylene oxide) triol, and MDI are disclosed in U.S. Pat. Nos. 4,225,696, 4,376,834, 4,436,896, and 4,551,498.